The development of techniques associated with mobile devices and increase in demand therefor have brought about rapid increase in the demand for secondary batteries as energy sources. Among secondary batteries, lithium secondary batteries with high energy density, high driving voltage and superior storage and lifespan characteristics are widely used as energy sources of various electric products including mobile devices.
Depending on the shape of the battery case, the secondary battery may be divided into cylindrical and rectangular batteries mounted in cylindrical and rectangular metal cans, respectively, and a pouch-shaped battery mounted in a pouch-shaped case made of an aluminum laminate sheet. Of these, the cylindrical battery has advantages of relatively high capacity and superior structural stability. The electrode assembly mounted in the battery case is an electricity-generating device enabling charge and discharge that has a cathode/separator/anode laminate structure and is divided into a jelly-roll type in which an electrode assembly including a separator interposed between a cathode and an anode, each made of an active material-coated long sheet, is rolled, a stack-type in which a plurality of cathodes and a plurality of anodes are laminated in this order such that a separator is interposed between the cathode and the anode and a stack/folding type which is a combination of a jelly-roll type and a stack type. Of these, the jelly-roll-type electrode assembly has advantages of easy manufacture and high energy density per unit weight.
In this regard, a conventional cylindrical secondary battery is shown in FIG. 1. An insulator generally used for the cylindrical secondary battery is shown in plan views of FIGS. 2 and 3.
Referring to FIGS. 2 and 3, a cylindrical secondary battery 100 is manufactured by mounting a jelly-roll type (rolled-type) electrode assembly 120 in a battery case 130, injecting an electrolyte into the battery case 130 and coupling a cap assembly 140 provided with an electrode terminal (for example, a cathode terminal; not shown) to the open top of the case 130.
The electrode assembly 120 is obtained by inserting a separator 123 between a cathode 121 and an anode 122, and rolling the resulting structure into a round shape. A cylindrical center pin 150 is inserted into the core (center) of the jelly-roll. The center pin 150 is generally made of a metal to impart a predetermined strength and has a hollow-shaped cylindrical structure of a roundly bent plate material. Such a center pin 150 sets and supports the electrode assembly and serves as a passage, enabling discharge of gas generated by internal reaction during charge and discharge, and operation.
In addition, a plate-shaped insulator 180a is mounted on the top of the electrode assembly 120, and is provided in the center thereof with an opening 181a communicating with the through hole 151 of the center pin 150 so that gas is discharged and the cathode tap 142 of the electrode assembly 120 is connected to the cap plate 145 of the cap assembly 140.
However, the insulator 180a arranged on the top of the jelly-roll is a structure that blocks a passage, enabling permeation of electrolyte into a battery in the process of injecting the electrolyte into the battery. For this reason, the electrolyte permeates the battery only through the opening 181a communicating with the center pin 150 and a region excluding the insulator 180a, thus disadvantageously requiring a long time for injection of electrolyte and consequently causing deterioration in productivity.
In order to improve permeability of the electrolyte, as shown in FIG. 3, a partial connection member 180b having a structure in which a plurality of through pores 182b are formed around an opening 181b is suggested.
However, this structure is found to have serious problems in terms of safety. That is, conductive impurity particles such as metal powders generated in the process of manufacturing and/or assembling the cap assembly 140, the battery case 130 and the like are permeated into the electrode assembly 120 through the through pores 182b that are perforated in the insulator 180b, thus disadvantageously causing occurrence of short circuit or deterioration in battery lifespan.
Accordingly, there is an increasing need for secondary batteries that enhance injection processability of electrolyte and prevent incorporation of foreign matter in the process of assembling batteries, thereby improving lifespan.